1. Field of the Invention
The invention generally relates to color filters having black matrixes, and to associated liquid crystal display (LCD) devices.
2. The Prior Art
In general, a monochrome or a color LCD device has the advantages of thinness, light weight and low power consumption. For this reason, LCD devices are widely used in various types of electronic equipment, from pocket calculators to large-scale office automation equipment.
Conventionally, a color LCD device includes a color filter at a position opposite to a liquid crystal layer. The color filter has three kinds of color (red, green and blue—RGB) resins separated by a black matrix having a plurality of apertures. The visibility of the LCD device mainly depends upon the characteristics of the black matrix of the color filter.
The basic structure of a conventional color LCD device is shown in FIG. 8. The LCD device 100 includes two glass substrates 14, 17 which cooperatively defining a chamber therebetween for receiving a liquid crystal layer 15. A plurality of columnar spacers 18 is distributed in the chamber for supporting of the two glass substrates 14, 17. The substrate 14, a color resin layer 12, a black matrix 13 and an ITO (Indium Tin Oxide) layer 11 collectively constitute a color filter. The color resin layer 12 includes RGB color resins respectively filled in apertures of the black matrix 13. The RGB color resins filter light beams passing therethrough, thus producing RGB color light beams.
The black matrix 13 functions as a light-shielding mask, to improve the contrast ratio of an LCD device using the color filter. In particular, a black matrix having an increased OD (Optical Density, i.e. light-shielding) value and having reduced optical reflectivity of top and bottom surfaces thereof is desired. However, the black matrix 13 is conventionally made from a metal whose optical reflectivity is too high, or is made from a resin whose OD value is too low. Thus, modified color filters have been developed to solve the above-described problems.
Referring to FIG. 9, a color filter as described in U.S. Pat. No. 6,285,424 issued on Sep. 4, 2001 is illustrated. The color filter 20 comprises a black matrix 23 formed on a transparent substrate 24. The black matrix 23 comprises a first antireflection film 231, a second antireflection film 232 and a metal screening film 233, formed one on top of the other in that order. The antireflection films 231, 232 are made of different kinds of metallic compounds having mutually different compositions. At least one of the films 231, 232, 233 contains chromium (Cr). In addition, RGB color resins 22 are separately filled in apertures of the black matrix 23. A protective layer 25 and a conductive layer 21 are sequentially formed on the RGB color resins 22 and the black matrix 23. The protective layer 25 functions as a layer flattening the color filter 20, and as an insulator.
In manufacturing of the color filter 20, firstly, the black matrix 23 having a plurality of apertures is formed on the transparent substrate 24 using exposing and developing technology. Then the RGB color resins 22 are repeatedly and respectively filled in the apertures of the black matrix 23, so that every three adjacent apertures have three different color resins and cooperatively define a pixel. Then the protective layer 25 is formed on the RGB color resins 22 and the black matrix 23, to provide an even outer surface for the color filter 20.
The multi-layer antireflection structure of the black matrix 23 can decrease the optical reflectivity of the surface thereof adjacent the transparent substrate 24. However, the optical reflectivity of the other surface thereof opposite to the transparent substrate 24 is still generally too great. That is, the optical reflectivity of the outer surface of the metal screening film 233 is too great. When the black matrix 23 is used in an LCD device, back light beams are reflected by the outer surface of the metal screening film 233 to an excessive degree. This creates light interference, which reduces the visibility of the LCD device. In addition, the multi-layer antireflection structure of the black matrix 23 only has two antireflection films 231, 232, giving the black matrix 23 insufficient ability to suppress reflections occurring on the surface thereof adjacent the transparent substrate 24.
Therefore, it is desired to obtain a color filter with low reflectivity on both surfaces thereof, and to obtain an LCD device incorporating such color filter.